Understanding the role of quaternary ammonium cations on the interaction of bitumen with clay:A molecular modeling study

JW Cao and Y Luo and HL Zhang and HH Duan, CONSTRUCTION AND BUILDING MATERIALS, 364, 129970 (2023).

DOI: 10.1016/j.conbuildmat.2022.129970

Bitumen-clay nanocomposites (BCNs) have been reported to display enhanced anti-ageing by forming intercalated or exfoliated structures. However, it remains a challenge to stabilize such fine clay tactoid in bitumen at high temperatures under static conditions. Intelligent and reliable modulation of the bitumen-clay interface to manufacture compatible and anti-ageing BCNs entails a physicochemical understanding of the interaction of clay and its derivatives with bitumen. In this paper, the density functional theory (DFT) and classical molecular dynamics (MD) are integrated for the first time to understand and design the interfaces between clay and bitumen. The affinity origin of bitumen with clay and its derivatives was well evaluated and consistent insights were found from different methodologies. The results show the binding strength of quaternary ammonium cations (QACs) with bitumen subfractions is asphaltenes > resins > aromatics > saturates. Furthermore, bitumen molecules are found to be stably adsorbed on clay surface with the help of cation- p interactions. The loaded QACs push asphaltenes with large molecular size away from the clay surface and few bitumen molecules can be co-adsorbed with QACs on clay surface when the QACs loading is 2.0 cation exchange capacity. The pull-out simulation shows the clays with 0.5 CEC and 1.0 CEC loadings are superior in binding to bitumen, while the interface stability of Na+-clay with bitumen is not weaker than organoclay. Ultimately, validation experiments supported our findings, showing that quaternary ammonium salts like CTAB have a ceiling in enhancing the interfacial affinity of bitumen with clay. This study updates previous biased understanding of bitumen-organoclay interactions and provides new guidance to moderate clay-bitumen interface, and this study constitutes a new paradigm by designing and validating the performance of BCNs.

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